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Tuesday, November 29, 2011

Intel Core i7 3960X (Sandy Bridge E) Review

If you look carefully enough, you may notice that things are changing. It first became apparent shortly after the release of Nehalem. Intel bifurcated the performance desktop space by embracing a two-socket strategy, something we'd never seen from Intel and only once from AMD in the early Athlon 64 days (Socket-940 and Socket-754).
LGA-1366 came first, but by the time LGA-1156 arrived a year later it no longer made sense to recommend Intel's high-end Nehalem platform. Lynnfield was nearly as fast and the entire platform was more affordable.
When Sandy Bridge launched earlier this year, all we got was the mainstream desktop version. No one complained because it was fast enough, but we all knew an ultra high-end desktop part was in the works. A true successor to Nehalem's LGA-1366 platform for those who waited all this time.

Left to right: Sandy Bridge E, Gulftown, Sandy Bridge
After some delays, Sandy Bridge E is finally here. The platform is actually pretty simple to talk about. There's a new socket: LGA-2011, a new chipset Intel's X79 and of course the Sandy Bridge E CPU itself. We'll start at the CPU.

LGA-2011, the new socket
For the desktop, Sandy Bridge E is only available in 6-core configurations at launch. Early next year we'll see a quad-core version. I mention the desktop qualification because Sandy Bridge E is really a die harvested Sandy Bridge EP, Intel's next generation Xeon part:

Sandy Bridge E die
If you look carefully at the die shot above, you'll notice that there are actually eight Sandy Bridge cores. The Xeon version will have all eight enabled, but the last two are fused off for SNB-E. The 32nm die is absolutely gigantic by desktop standards, measuring 20.8 mm x 20.9 mm (~435mm^2) Sandy Bridge E is bigger than most GPUs. It also has a ridiculous number of transistors: 2.27 billion.
Around a quarter of the die is dedicated just to the chip's massive L3 cache. Each cache slice has increased in size compared to Sandy Bridge. Instead of 2MB, Sandy Bridge E boasts 2.5MB cache slices. In its Xeon configuration that works out to 20MB of L3 cache, but for desktops it's only 15MB. That's just 1MB shy of how much system memory my old upgraded 386-SX/20 had.
CPU Specification Comparison
CPUManufacturing ProcessCoresTransistor CountDie Size
AMD Bulldozer 8C32nm8~2B315mm2
AMD Thuban 6C45nm6904M346mm2
AMD Deneb 4C45nm4758M258mm2
Intel Gulftown 6C32nm61.17B240mm2
Intel Sandy Bridge E (6C)32nm62.27B435mm2
Intel Nehalem/Bloomfield 4C45nm4731M263mm2
Intel Sandy Bridge 4C32nm4995M216mm2
Intel Lynnfield 4C45nm4774M296mm2
Intel Clarkdale 2C32nm2384M81mm2
Intel Sandy Bridge 2C (GT1)32nm2504M131mm2
Intel Sandy Bridge 2C (GT2)32nm2624M149mm2
At the core level, Sandy Bridge E is no different than Sandy Bridge. It doesn't clock any higher, L1/L2 caches remain unchanged and per-core performance is identical to what Intel launched earlier this year.

The Lineup
 

ProcessorCore ClockCores / ThreadsL3 CacheMax TurboMax Overclock MultiplierTDPPrice
Intel Core i7 3960X3.3GHz6 / 1215MB3.9GHz57x130W$990
Intel Core i7 3930K3.2GHz6 / 1212MB3.8GHz57x130W$555
Intel Core i7 38203.6GHz4 / 810MB3.9GHz43x130WTBD
Intel Core i7 2700K3.5GHz4 / 88MB3.9GHz57x95W$332
Intel Core i7 2600K3.4GHz4 / 88MB3.8GHz57x95W$317
Intel Core i7 26003.4GHz4 / 88MB3.8GHz42x95W$294
Intel Core i5 2500K3.3GHz4 / 46MB3.7GHz57x95W$216
Intel Core i5 25003.3GHz4 / 46MB3.7GHz41x95W$205
Those of you buying today only have two options: the Core i7-3960X and the Core i7-3930K. Both have six fully unlocked cores, but the 3960X gives you a 15MB L3 cache vs. 12MB with the 3930K. You pay handsomely for that extra 3MB of L3. The 3960X goes for $990 in 1K unit quantities, while the 3930K sells for $555.
The 3960X has the same 3.9GHz max turbo frequency as the Core i7 2700K, that's with 1 - 2 cores active. With 5 - 6 cores active the max turbo drops to a respectable 3.6GHz. Unlike the old days of many vs. few core CPUs, there are no tradeoffs for performance when you buy a SNB-E. Thanks to power gating and turbo, you get pretty much the fastest possible clock speeds regardless of workload. 
Early next year we'll see a Core i7 3820, priced around $300, with only 4 cores and a 10MB L3. The 3820 will only be partially unlocked (max OC multiplier = 4 bins above max turbo).

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